ch22_arom

CHAPTER 22 ~ INDUCTION AND ALTERNATING CURRENT!

KEY VARIABLES:
A: Area of the loop
B: strength of the magnetic field (T)
$\displaystyle \Delta{t}$ : time (s)
N: number of turns in the coil (turns)
$\displaystyle \Delta{V_{rms}}$ : root-mean-square potential difference
$\displaystyle \Delta{V}$ : potential difference (V)
P: power (W)

KEY EQUATIONS:
$\displaystyle emf=-N\frac{\Delta(ABcos\theta)}{\Delta{t}}$
$\displaystyle \Delta{V_{rms}}=\frac{\Delta V_{max}}{\sqrt{2}}=0.707{\Delta{V_{max}}}$
$\displaystyle I_{rms}=\frac{I_{max}}{\sqrt{2}}=0.707{I_{max}}$
$\displaystyle \Delta{V_2}=\frac{N_2}{N_1}\Delta{V_1}$ : this can also be looked at as a proportion :
$\displaystyle \frac{N_1}{N_2}=\frac{V_1}{V_2}$
$\displaystyle P_1=P_2$
$\displaystyle \Delta{V_1}I_1=\Delta{V_2}I_2$

KEY CONCEPTS:
SECTION 22-1

• Moving a conductor in an electric field or changing the magnetic field around a conductor will induce an emf (electromotive force) in the conductor through electromagnetic induction.
• The charges already present in the conductor will be caused to move in opposite directions by the motion of the conductor through the field, therefore a current can be induced without a battery or other source present.
• When a loop/coil of wire is moved linearly through a magnetic field the orientation of the loop will affect the current induced.
  • If the plane of the loop is perpendicular to the magnetic field, the current is greatest.
  • If the plane of the loop is parallel to the magnetic field, the current is zero.
• If more magnetic field lines are cut by the loop of wire, the emf increases.
• Lenz's law states that the magnetic field of the induced current opposes the change in the applied magnetic field.

SECTION 22-2

• Generators use induction to convert mechanical energy to electrical energy.
• A continuously changing emf is produced by a rotating coil of wire inside a uniform magnetic field.
• When the loop is perpendicular to the magnetic field, every portion of the loop is moving parallel to the magnetic field so no current is induced.
• When the loop is parallel to the magnetic field, the sides of the loop are crossing the largest number of magnetic field lines so the largest emf is produced.
• Alternating current is when the emf varies from zero to the maximum twice every rotation of the coil and follows a sinusoidal path.
• The maximum potential difference is only reached during a small part of each cycle.
• The effective potential difference is the square root of the average of the square of the potential difference over time (root-mean-square potential difference).
• Electrical meters usually read rms values for alternating current.
• Motors use an arrangement similar to generators to convert electrical energy to mechanical energy (the opposite of what a generator does).

SECTION 22-3

• Mutual inductance involves the induction of a current in one circuit by means of changing current in another circuit (seen most often as a transformer).
• Two coils of wire wound on the same iron core changes the potential difference of an alternating current source.
• The power produced by the output of a transformer is the same as the power consumed by the transformer.

The organization and overall structure match the 2002 edition of Holt Physics by Serway and Faughn and many of the expressions and the ideas come from there as well. Much of wording and ideas also come from Honors Physics Review Notes 2008-2009 by Strong.

Citations:

Faughn, Jerry S. and Raymond A. Serway. Holt Physics. New York, Holt. 2002.
Strong, Tom. Course notes. Honors Physics. Dept. of Science. Mt Lebanon High School. May and June 2009.